1. Field of the Invention
The present invention relates to a battery, such as a lithium ion or lithium polymer battery, in which a battery element working as a power generation element is stored in a housing, and power generated by the battery element is output from a pair of positive and negative terminals.
2. Description of the Related Art
In recent years, the demand for information devices, such as notebook personal computers, mobile communication devices such as cellular phones, portable electronic devices such as video cameras, digital still cameras, and portable audio devices has been rapidly increased. As power sources for such electronic devices, small closed-type secondary batteries, such as nickel cadmium batteries, nickel hydrogen batteries, and lithium ion batteries, are employed in various fields by virtue of their characteristics, such as high voltage, high energy density, and lightweight.
In particular, polymer lithium ion secondary batteries are used as batteries taking measures to prevent liquid leakage that poses problems when a liquid electrolyte is used. Such batteries include a type using a gel-like polymer membrane formed by impregnating a nonaqueous electrolyte into a polymer, and a type using a totally solid state electrolyte.
Polymer lithium ion secondary batteries of the above-described type have battery characteristics, such as high energy density, and lightweight. For these batteries, further technological development is being progressed to satisfy needs in recent years for, for example, miniaturization, lightweight, thinning of various electronic devices by taking advantage the above-described characteristics as well as characteristics in terms of a high degree of freedom in battery shape.
Among polymer lithium ion secondary batteries, one type being popularly used is manufactured in the following manner. A battery cell including a laminate-structured battery element is formed; and the battery cell is connected to a circuit board including components, such as electrode terminals, and then is stored with the electrolyte into a metallic container. Among lithium-ion secondary battery, one type being popularly used is manufactured in the following manner. A battery cell is formed and stored with the electrolyte in a metallic container, and a printed circuit board including positive and negative terminal portions is coupled to positive and negative electrodes formed on an end face of the battery cell; and an assembly thus formed is stored into a plastic housing or the like. In this case, the battery cell further includes a protection device such as a PTC component (PTC: positive temperature coefficient) that is used for charge control, safety control, and the like by detecting the temperature and shuts down and controls an input/output circuit.
For such lithium ion secondary batteries, the demand about, for example, miniaturization of the whole battery and increasing of the battery capacity is increased in association with the progress in functional enhancement and miniaturization of portable electronic devices. The miniaturization of the whole battery is relatively easily accomplishable by miniaturization of, for example, the battery and the battery housing. On the other hand, however, a desired battery capacity cannot be obtained when the battery element is miniaturized. In contrast, in the case where the battery element and the battery cell that encloses the battery element are, respectively, large, while the capacity can be increased, the whole battery has to be enlarged. However, in the case where the capacity of the battery cell is increased while preventing enlargement of the whole battery, the battery housing has to be thinned, such that a sufficient mechanical strength of the battery cannot be obtained. This can potentially leads to undesired incidents, such as deformation and damaging, caused by, for example, a fall accident and an environmental change, such as a temperature change under compression forces being exerted by an urging member provided on the side of the electronic device.